Heat oven to 350. Lightly grease a 9 x 13 inch baking dish.
In a sauce pan combine 3 cups blueberries, sugar, cornstarch, and lemon juice. Stir over medium low heat until the blueberries start to release their own juices. This will take about 5-6 minutes.
Increase the heat to medium high heat. Bring to a boil, stirring constantly for about 1 1/2 minutes.
Add in the other 2 cups of blueberries, vanilla, and butter. Keep stirring until the butter is melted.
Let the blueberry mixture cool as you make the crust.
In a stand mixer or mixing bowl combine the flour, sugar, brown sugar, baking powder, cornstarch, and salt. Pulse until all is combined.
Spread the butter chunks over the flour mixture in the bowl. Continue to pulse until it forms into coarse crumbs.
Add in egg and vanilla and continue to stir until it all clings together.
Place half of the mixture into the bottom of your prepared pan. Spread evenly with your fingers or the back of a spoon.
Then spoon the blueberry mixture over the crust and spread evenly over all.
Bake for about 35 minutes or until the crumb topping is golden.
Let the bars cool and make the glaze.
Mix together the powdered sugar, vanilla, almond extract, and milk.
When all combined drizzle over the cooled bars. (You can drizzle over warm bars, but the drizzle might run together.) Slice and serve.